(1) Field of the Invention
The present invention relates to a sheet post-processing device folding a sheet output from an image forming device, and a sheet folding method.
(2) Related Art
A sheet post-processing device having a sheet folding function to fold a printed sheet output from an image forming device, such as a printer, by a job performed by the image forming device has been developed. For example, the printed sheet is folded in two by being folded in the middle thereof in a sheet conveyance direction, and is folded in three by being folded at two different positions in the sheet conveyance direction.
An example of such a sheet post-processing device is a sheet post-processing device including a folding roller pair disposed along a sheet conveyance path that slopes downward, a knife-shaped push plate disposed opposite the folding roller pair across the conveyance path, and a stopper disposed at a lower end portion of the conveyance path and is movable along the conveyance path.
At the time of folding a sheet, for each sheet size, the stopper is moved so that the sheet faces an edge of the push plate at a target fold position on the sheet in a state where the sheet is stopped with a lower edge thereof being in contact with the stopper. The push plate is then moved to perform a pushing operation to push the sheet into a nip of the folding roller pair at the target fold position on the sheet in a state where the edge of the push plate is in contact with the sheet at the target fold position on the sheet.
A sheet post-processing device including a movable stopper as described above, however, adds to the complexity and cost of the device.
Such problems arise not only when the device has a configuration in which a sheet to be used is selected from among sheets having different sizes, but also when the device has a configuration in which, for each sheet having the same size, whether to fold the sheet in two or in three, which differ in a fold position, is switched.